查询词典 Nature

The effect of tribology factors on bearing vibration is studied experimentally. AR model and WPT are used to processing the normal arid abnormal signals. The results are as follows:1. The vibration of ball bearings is caused by the tribology action of contact pairs of ball and ring races and has the essential of tribo-dynamics. Any factors affecting the tribology characteristics of contact pairs will affect vibration and noise of bearings consequently.2. Vibration characteristics of bearing keep almostly unchanged with the increasing of axial load expecting the increasing of nature frequencies. When radial load increasing with axial load unchanged, nature frequencies keep unchanged but some new vibration peaks appears in the spectrum.3. Vibration amplitudes are damped and nature frequency are enhanced with sufficient lubrication. Vibration and noise of bearings increase obviously and roar can happen and the contact surfaces scratch slightly under insufficient and unclean lubrication state. Bearing will be disabled in a few minutes without any lubrication.4. Bearing vibration is unstable under low speed. With the speed increasing, the vibration become stable and natural frequencies increase slightly but the amplitudes increase apparently.5. Bearing vibration can be excited only by some harmonics ofwaviness without lubrication and by all harmonics with lubrication based on the theoretical analysis.6. The nature frequencies of ball bearings decrease with the increasing sizes. When international clearance increasing, nature frequencies decrease in radial and increase in axial and angular and the amplitudes increase in radial and decrease in axial and angular. When the number of balls increasing, nature frequencies increase and amplitudes decrease. When the pitch diameter increasing, axial nature frequency increase and others nearly keep no change. When outer race groove curvature radius increasing, nature frequencies increase in radial and decrease in axial and angular and amplitudes keep no change in radial and increase in axial and angular. When inner race groove curvature radius increasing, nature frequencies decrease and amplitudes increase.7. The distortion in amplitude and frequency components of bearing vibration signals picked up by the present probe measurement method is founded and right conclusions cannot be achieved by the signals. When accelerometer is rigidly screwed with steel stud onto a flat outer surface of a ball bearing, vibration signal can be got without distortion and the reliability of research on bearing vibration is assured.8. AR model is suitable for large samples of bearing vibration signals, square root of length of samples can be used as the upper limitation of order determination and the FPE order selection criterion is effective. Many advantages of AR spectrum are founded over the classical based on FFT.9. Time-Frequency analysis is necessary for abnormal noise of ball bearings. WPT overcomes the principle shortcomings of STFT and proved to be a best tool to process the abnormal signals.

理论分析和试验研究表明： 1球轴承振动是钢球—滚道接触副中的各种摩擦学作用引起的，具有摩擦动力学的本质，任何对接触副的摩擦学特性有影响的因素都将对球轴承的振动和噪声特性产生影响； 2中心轴向载荷作用下，载荷增大使球轴承的固有振动频率升高，载荷越大同样的载荷增幅引起的频率升幅减小，足够大的中心轴向载荷作用下载荷的变化对球轴承振动的频率特性不会产生明显的影响； 3轴向和径向联合载荷作用下，径向载荷不大时球轴承振动的固有频率基本不变，但是可能引起变刚度激励的非线性振动，出现新的频峰，过大的径向载荷将使部分钢球脱离接触，使球轴承的振动和噪声呈现不稳定状态； 4润滑对球轴承的振动和噪声特性有重要的影响，良好的润滑对振动有明显的抑制作用，润滑不充分时，振动和噪声的水平会有明显增高，一定条件下还会激发接触副中的谐振，发出啸声，造成接触表面的伤害，无润滑干接触时，短时的运转就会损伤接触副表面，使振动和噪声迅速增大，并随时可能引发严重的磨损和卡滞失效；接触副润滑良好时，油膜的"刚化效应"使球轴承振动的固有频率有所提高，润滑剂中含有弥散性污浊时，振动的幅度总体升高，但弥散性污浊不会改变球轴承振动的频率特性；浙江大学博士学位论文：球轴承振动的研究 5低速时，球轴承振动的基本特征呈现不稳定状态，随着转速的提高，球轴承振动的频率特性趋于稳定，固有频率频峰升高； 6理论分析表明，干接触时钢球和滚道表面波纹度的某些谐波分量能激励球轴承的振动，振动的幅值与谐波幅值成正比，实际球轴承中钢球的分布不可能完全均匀，波纹度的激励作用会随时发生；润滑接触的分析表明，波纹度的任意谐波分量均能激励球轴承的振动； 7球轴承的几何和结构参数分析表明，球轴承尺寸越大，径向、轴向和角振动的固有频率越低；钢球中心圆直径增大，球轴承的径向和轴向振动的固有频率基本不变，角振动的固有频率有所上升，振动的幅频特性基本不变；径向游隙加大使球轴承的径向振动固有频率降低，轴向和角振动的固有频率有所升高，径向振动幅频特性的幅值升高，而轴向和角向降低；钢球的数量增多使球轴承振动的固有频率上升，幅频特性的幅值下降，径向振动的幅值下降最为明显；外圈沟曲率半径系数增大使球轴承径向振动的固有频率升高，轴向和角振动的固有频率降低，径向幅频特性基本不变，轴向和角向幅频特性幅值升高；内圈沟曲率半径系数增大使径向、轴向和角振动固有频率均下降，振动幅频特性的幅值均有升高； 8试验对比表明，传感器采用探针式安装时，由于探针接触副接触特性的影响，钡(量得到的球轴承振动信号有失真，采用专门设计和制作的试验球轴承，以固定式安装加速度计，首次测量得到了球轴承振动的真实信号，通过对振动信号的分析，验证了球轴承振动的理论模型； 9)基于时间序列分析的AR模型适用于大样本球轴承振动信号的分析，以样本长度的均方根值作定阶上界，FPE做判阶准则，给出的AR谱光滑，频率分辨率高，是球轴承振动分析的简便而可靠的手段； 10以时频域分析的小波包变换分析球轴承异音信号能够比较好地定位和聚焦异音发生的时间，时间间隔，频率范围，同样是球轴承振动分析的可靠的手段，可用作球轴承故障诊断技术。

Writing in the journal Nature, they said that the squirrels' screeches appear to be the first known example of ultrasonic alarm calls in an animal.

在Nature期刊上，他们说松鼠的叫声似乎是动物界第一个已知的利用超音波的例子。

These taste great and are fun shapes for kids. However if you are giving your child two a day, then the Nature's Plus chewable Vitamin C is a good choice.

这是孩子们喜欢的好吃的味道和非常有趣的形状，但是如果你是给你的孩子每天两次，那么 Nature's Plus的维生素C咀嚼片是一个很好的选择。

The topic "the categories of being" is intermediate between the topic "the nature of being" and the topics that fall under the post-Medieval conception of metaphysics for a reason that can be illustrated by considering the problem of universals.

&being的范畴&这个主题是&being的nature&和那些中世纪后的形上学的主题（&universals『共相』的问题&所表达的主题）中间的主题。

In addition to these three topics—the nature of being; the first causes of things; things that do not change—(the latter two being understood as including attempts to show that there no first causes or things that do not change), the topics that fall under the "old" or "Aristotelian/Medieval" conception of metaphysics, we must recognize attention to a large range of "new" or "post-Medieval" topics as no less the proper business of metaphysics than these three.

除开这三个&旧&或&Aristotle/中世纪&形上学主题——being的nature，诸第一因，不变东西（后两个被理解为包括试图指出不存在这样的东西）——那些&新&或&中世纪后&的形上学主题，并不比这三个更少正当性。

Nature change and so do the natures nd if you do not change,get ready to extinct.

Nature的变化，因此这样做的性质次如果你不改变，准备灭绝。

One response sometimes made to this argument is that it is correct as an account of our concept of the mind, but not correct about the actual nature of the mind.13 Reality is, so to speak, deconstructive of the concept that we have.

对这个论证有时有一个回应是：这作为对我们的心灵概念的一个说明，是对的；但对心灵的实际nature来说，不对。[13] 按此说，实在解构了我们拥有的概念。

Product description:With a light herbal-y scent, California Baby Calendula Lotion works to soothe and heal skin naturally effective that we call it, Nature' First-Aid Calendula is commonly known as the common Pot Marigold flower and has been used to safely soothe and heal skin for centuries.

产品描述：加州宝宝的金盏草乳液含有我们称为Nature's First Aid的金盏草的精华，一般来说，叫金盏花，这个花朵，几个世纪以来一直安全的用来舒缓和治疗皮肤。

Product description产品描述:With a light herbal-y scent, California Baby Calendula Lotion works to soothe and heal skin naturally effective that we call it, Nature' First-Aid Calendula is commonly known as the common Pot Marigold flower and has been used to safely soothe and heal skin for centuries.

含有淡淡的草本气味，加州宝宝的金盏草乳液含有我们称为Nature's First Aid的金盏草的精华，一般来说，叫金盏花，这个花朵，几个世纪以来一直安全的用来舒缓和治疗皮肤。

Guests can also visit the rare eagle in the Philippine Eagle Research and Nature Centre, located in Malagos, Calinan, which is 45 minutes from downtown Davao City.

游客如有兴趣一睹罕有的菲律宾大鹰，可到位於Malagos， Calinan的野生大鹰研究及自然保育中心(Philippine Eagle Research and Nature Centre)，从达沃市中心出发大约45分钟车程。

With Death guitarist Schuldiner adopting vocal duties, the band made a major impact on the scene.

随着死亡的吉他手Schuldiner接受主唱的职务，乐队在现实中树立了重要的影响。

But he could still end up breakfasting on Swiss-government issue muesli because all six are accused of nicking around 45 million pounds they should have paid to FIFA.

不过他最后仍有可能沦为瑞士政府&议事餐桌&上的一道早餐，因为这所有六个人都被指控把本应支付给国际足联的大约4500万英镑骗了个精光。